At least 5,600 supporters of so-called Islamic State (IS) have returned to their home countries as it loses ground in Iraq and Syria, a new report says.
The Soufan Center, a US-based think tank, says 33 states have reported arrivals in the past two years.
The figure includes half of the estimated 850 people who left the UK.
The report says the returnees – most of whom are imprisoned or disappear from view – will continue to present a security challenge for years to come.
IS has lost much of the territory that once made up the “caliphate” it proclaimed in June 2014, attracting thousands of jihadists from across the world.
Last week, US-backed alliance of Syrian Kurdish and Arab fighters said they had taken full control of Raqqa, the jihadists’ de facto capital.
The Soufan Center’s report says the flow of foreign fighters came to a virtual standstill in late 2015, as IS began to suffer defeats and states implemented better measures to prevent travel.
Added to the unknown numbers from other countries, this represents a huge challenge for security and law enforcement entities, according to the report.
“Although there is disagreement over the threat that returning foreign fighters may present to their countries of residence or origin, or to other countries they pass through, it is inevitable that some will remain committed to the form of violent ‘jihad’,” it says.
The report warns that as the territorial “caliphate” shrinks and is increasingly denied an overt presence, the IS leadership is highly likely to look to supporters overseas, including returnees, to “keep the brand alive”.
“Returnees may be particularly vulnerable to contact from people who were part of the network that recruited them, or appeals for help from ex-comrades in arms.”
